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Spatial crop nitrogen (N) management has advanced over the years by using canopy reflectance data to make N recommendations. But the value of an automated system for variable-rate applications (VRA) has not been extensively demonstrated in cotton. This study evaluated the performance of an integrated system for on-the-go VRA at a 1-m spatial resolution in two different field trials in 2016 and 2017. The VRA system applied consistently less fertilizer N than the farmer practice, 42% and 33% less total N in the 2016 and 2017 field trials, respectively. Despite the reduced N inputs, increased energy-use efficiency (EUE) by 16% and return to N cost by €81/ha in 2016, VRA still over-applied N because of lack of yield response to N fertilizer. In the 2017 field, VRA yield gains by 5–8% over the farmer practice were not statistically significant and came about after cotton regrowth due to a bollworm infestation. With or without a back-off function in effect, VRA delivered an Economic Optimum N Rate, greatly increased N recovery by 12–22%, EUE by 26% and net return to N by €190–248/ha in comparison to the farmer. The reduction of N inputs also improved coupling of the soil-crop N cycle by reducing the effects of excess farmer application on soil acidity, electrical conductivity and residual nitrates in the root zone. Under the field conditions of this study, implementation of the high-resolution VRA can result in environmental and economic benefits especially in non-problematic fields where the crop responds to N fertilization. [ABSTRACT FROM AUTHOR]

The effects of land use changes on the ecology and hydrology of natural watersheds have long been debated. However, less attention has been given to the hydrological effects of forest roads. Although less studied, several researchers have claimed that streamflow changes related to forest roads can cause a persistent and pervasive effect on hillslope hydrology and the functioning of the channel system. The main potential direct effects of forest roads on natural watersheds hydrologic response are runoff production on roads surfaces due to reduced infiltration rates, interruption of subsurface flow by road cutslopes and rapid transfer of the produced runoff to the stream network through roadside ditches. The aforementioned effects may significantly modify the total volume and timing of the hillslope flow to the stream network. This study uses detailed field data, spatial data, hydro-meteorological records, as well as numerical simulation to investigate the effects of forest roads on the hydrological response of a small-scale mountain experimental watershed, which is situated in the east side of Penteli Mountain, Attica, Greece. The results of this study highlight the possible effects of forest roads on the watersheds hydrological response that may significantly influence direct runoff depths and peak flow rates. It is demonstrated that these effects can be very important in permeable watersheds and that more emphasis should be given on the impact of roads on the watersheds hydrological response. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The Soil Conservation Service Curve Number (SCS-CN) method is widely used for predicting direct runoff volume for a given rainfall event. The applicability of the SCS-CN method and the runoff generation mechanism were thoroughly analysed in a Mediterranean experimental watershed in Greece. The region is characterized by a Mediterranean semi-arid climate. A detailed land cover and soil survey using remote sensing and GIS techniques, showed that the watershed is dominated by coarse soils with high hydraulic conductivities, whereas a smaller part is covered with medium textured soils and impervious surfaces. The analysis indicated that the SCS-CN method fails to predict runoff for the storm events studied, and that there is a strong correlation between the CN values obtained from measured runoff and the rainfall depth. The hypothesis that this correlation could be attributed to the existence of an impermeable part in a very permeable watershed was examined in depth, by developing a numerical simulation water flow model for predicting surface runoff generated from each of the three soil types of the watershed. Numerical runs were performed using the HYDRUS-1D code. The results support the validity of this hypothesis for most of the events examined where the linear runoff formula provides better results than the SCS-CN method. The runoff coefficient of this formula can be taken equal to the percentage of the impervious area. However, the linear formula should be applied with caution in case of extreme events with very high rainfall intensities. In this case, the medium textured soils may significantly contribute to the total runoff and the linear formula may significantly underestimate the runoff produced. [ABSTRACT FROM AUTHOR]

While pipe selection for collective irrigation networks, in the framework of optimal design, is based on methods that have been successfully developed and applied, it is often given insufficient attention in the case of simple irrigation systems. In these projects, designers use very simple empirical pipe selection methods based on arbitrary concepts, which do not lead to an optimal solution. In this article, a simple method is presented, which allows the user to determine directly the optimum pipe size to use in simple irrigation delivery systems with pumps. A detailed theoretical analysis of the behavior of the total cost variable (energy and pipe cost per unit length), expressed as a function of discharge for the various available diameters, was carried out. The proposed method led to the derivation of a simple equation from which the critical values of discharge corresponding to the available pipe diameters are explicitly calculated. The direct computational optimal solution is demonstrated in application examples. The examples used in this application are systems with horizontal and sloping topography with identical outlets (same discharge and pressure head) or systems having outlets with various pressure heads. For simple, non-looping, irrigation delivery systems (single main or submain delivery pipeline), it is sufficient to directly calculate the values of critical discharge corresponding to the various available commercial diameters using the proposed equation. For sloping or branched delivery networks, the equation is applied to the critical path portion of the network that is affected by the energy cost. For the rest of the system, the design is based on hydraulic criteria only. Comparison with previous empirical explicit methods indicates good performance by this new method. [ABSTRACT FROM AUTHOR]

The ecological integrity of rivers ultimately depends on flow regime. Flow degradation is especially prominent in Mediterranean systems and assessing environmental flows in modified rivers is difficult, especially in environments with poor hydrologic monitoring and data availability. In many Mediterranean countries, which are characterized by pronounced natural variability and low summer flows, water management actions usually focus on prescribing minimum acceptable flows estimated by hydrologic methods. In this study, a comparative assessment of environmental flow estimation methods is developed in a river with poorly monitored flows and limited understanding of past reference conditions. This assessment incorporates both a hydrologic and a fish habitat simulation effort that takes into consideration hydrologic seasonality in a Greek mountainous river. The results of this study indicate that especially in data scarce regions the utilization of biotic indicators through habitat models, may provide valuable information, beyond that achievable with hydrologic methods, for developing regional environmental flow criteria. Despite the widespread use of the method, challenges in transferability of fish habitat simulation provide undefined levels of uncertainty and may require the concurrent use of different assessment tools and site-specific study.